Disable aging when doing deadlock detection GC

rts/Schedule.c

@@ -164,7 +164,8 @@ static void scheduleHandleThreadBlocked( StgTSO *t );
 static bool scheduleHandleThreadFinished( Capability *cap, Task *task,
                                           StgTSO *t );
 static bool scheduleNeedHeapProfile(bool ready_to_gc);
-static void scheduleDoGC(Capability **pcap, Task *task, bool force_major);
+static void scheduleDoGC( Capability **pcap, Task *task,
+                          bool force_major, bool deadlock_detect );
 
 static void deleteThread (StgTSO *tso);
 static void deleteAllThreads (void);
@@ -264,7 +265,7 @@ schedule (Capability *initialCapability, Task *task)
     case SCHED_INTERRUPTING:
         debugTrace(DEBUG_sched, "SCHED_INTERRUPTING");
         /* scheduleDoGC() deletes all the threads */
-        scheduleDoGC(&cap,task,true);
+        scheduleDoGC(&cap,task,true,false);
 
         // after scheduleDoGC(), we must be shutting down.  Either some
         // other Capability did the final GC, or we did it above,
@@ -561,7 +562,7 @@ run_thread:
     }
 
     if (ready_to_gc || scheduleNeedHeapProfile(ready_to_gc)) {
-      scheduleDoGC(&cap,task,false);
+      scheduleDoGC(&cap,task,false,false);
     }
   } /* end of while() */
 }
@@ -935,7 +936,7 @@ scheduleDetectDeadlock (Capability **pcap, Task *task)
         // they are unreachable and will therefore be sent an
         // exception.  Any threads thus released will be immediately
         // runnable.
-        scheduleDoGC (pcap, task, true/*force major GC*/);
+        scheduleDoGC (pcap, task, true/*force major GC*/, true/*deadlock detection*/);
         cap = *pcap;
         // when force_major == true. scheduleDoGC sets
         // recent_activity to ACTIVITY_DONE_GC and turns off the timer
@@ -1005,7 +1006,7 @@ scheduleProcessInbox (Capability **pcap USED_IF_THREADS)
     while (!emptyInbox(cap)) {
         // Executing messages might use heap, so we should check for GC.
         if (doYouWantToGC(cap)) {
-            scheduleDoGC(pcap, cap->running_task, false);
+            scheduleDoGC(pcap, cap->running_task, false, false);
             cap = *pcap;
         }
 
@@ -1552,9 +1553,11 @@ void releaseAllCapabilities(uint32_t n, Capability *keep_cap, Task *task)
  * Perform a garbage collection if necessary
  * -------------------------------------------------------------------------- */
 
+// N.B. See Note [Deadlock detection under nonmoving collector] for rationale
+// behind deadlock_detect argument.
 static void
 scheduleDoGC (Capability **pcap, Task *task USED_IF_THREADS,
-              bool force_major)
+              bool force_major, bool deadlock_detect)
 {
     Capability *cap = *pcap;
     bool heap_census;
@@ -1847,9 +1850,9 @@ delete_threads_and_gc:
     // emerge they don't immediately re-enter the GC.
     pending_sync = 0;
     signalCondition(&sync_finished_cond);
-    GarbageCollect(collect_gen, heap_census, gc_type, cap, idle_cap);
+    GarbageCollect(collect_gen, heap_census, deadlock_detect, gc_type, cap, idle_cap);
 #else
-    GarbageCollect(collect_gen, heap_census, 0, cap, NULL);
+    GarbageCollect(collect_gen, heap_census, deadlock_detect, 0, cap, NULL);
 #endif
 
     // If we're shutting down, don't leave any idle GC work to do.
@@ -2723,7 +2726,7 @@ exitScheduler (bool wait_foreign USED_IF_THREADS)
         nonmovingStop();
         Capability *cap = task->cap;
         waitForCapability(&cap,task);
-        scheduleDoGC(&cap,task,true);
+        scheduleDoGC(&cap,task,true,false);
         ASSERT(task->incall->tso == NULL);
         releaseCapability(cap);
     }
@@ -2791,7 +2794,7 @@ performGC_(bool force_major)
     // TODO: do we need to traceTask*() here?
 
     waitForCapability(&cap,task);
-    scheduleDoGC(&cap,task,force_major);
+    scheduleDoGC(&cap,task,force_major,false);
     releaseCapability(cap);
     boundTaskExiting(task);
 }

rts/sm/Evac.c

@@ -85,7 +85,12 @@ alloc_for_copy (uint32_t size, uint32_t gen_no)
         }
     }
 
-    if (RtsFlags.GcFlags.useNonmoving && gen_no == oldest_gen->no) {
+    if (RtsFlags.GcFlags.useNonmoving) {
+        /* See Note [Deadlock detection under nonmoving collector]. */
+        if (deadlock_detect_gc)
+            gen_no = oldest_gen->no;
+
+        if (gen_no == oldest_gen->no) {
             gct->copied += size;
             to = nonmovingAllocate(gct->cap, size);
 
@@ -98,10 +103,17 @@ alloc_for_copy (uint32_t size, uint32_t gen_no)
                 ws->todo_seg = seg;
             }
 
-        if (major_gc)
+            // The object which refers to this closure may have been aged (i.e.
+            // retained in a younger generation). Consequently, we must add the
+            // closure to the mark queue to ensure that it will be marked.
+            //
+            // However, if we are in a deadlock detection GC then we disable aging
+            // so there is no need.
+            if (major_gc && !deadlock_detect_gc)
                 markQueuePushClosureGC(&gct->cap->upd_rem_set.queue, (StgClosure *) to);
             return to;
         }
+    }
 
     ws = &gct->gens[gen_no];  // zero memory references here
 
@@ -319,7 +331,10 @@ evacuate_large(StgPtr p)
    */
   new_gen_no = bd->dest_no;
 
-  if (new_gen_no < gct->evac_gen_no) {
+  if (deadlock_detect_gc) {
+      /* See Note [Deadlock detection under nonmoving collector]. */
+      new_gen_no = oldest_gen->no;
+  } else  if (new_gen_no < gct->evac_gen_no) {
       if (gct->eager_promotion) {
           new_gen_no = gct->evac_gen_no;
       } else {
@@ -370,7 +385,7 @@ evacuate_static_object (StgClosure **link_field, StgClosure *q)
 {
     if (RTS_UNLIKELY(RtsFlags.GcFlags.useNonmoving)) {
         // See Note [Static objects under the nonmoving collector] in Storage.c.
-        if (major_gc)
+        if (major_gc && !deadlock_detect_gc)
             markQueuePushClosureGC(&gct->cap->upd_rem_set.queue, q);
         return;
     }
@@ -615,7 +630,7 @@ loop:
           // NOTE: large objects in nonmoving heap are also marked with
           // BF_NONMOVING. Those are moved to scavenged_large_objects list in
           // mark phase.
-          if (major_gc)
+          if (major_gc && !deadlock_detect_gc)
               markQueuePushClosureGC(&gct->cap->upd_rem_set.queue, q);
           return;
       }
@@ -647,7 +662,7 @@ loop:
           // We may have evacuated the block to the nonmoving generation. If so
           // we need to make sure it is added to the mark queue since the only
           // reference to it may be from the moving heap.
-          if (major_gc && bd->flags & BF_NONMOVING) {
+          if (major_gc && bd->flags & BF_NONMOVING && !deadlock_detect_gc) {
               markQueuePushClosureGC(&gct->cap->upd_rem_set.queue, q);
           }
           return;
@@ -661,7 +676,7 @@ loop:
           // We may have evacuated the block to the nonmoving generation. If so
           // we need to make sure it is added to the mark queue since the only
           // reference to it may be from the moving heap.
-          if (major_gc && bd->flags & BF_NONMOVING) {
+          if (major_gc && bd->flags & BF_NONMOVING && !deadlock_detect_gc) {
               markQueuePushClosureGC(&gct->cap->upd_rem_set.queue, q);
           }
           return;
@@ -965,7 +980,7 @@ evacuate_BLACKHOLE(StgClosure **p)
     ASSERT((bd->flags & BF_COMPACT) == 0);
 
     if (bd->flags & BF_NONMOVING) {
-        if (major_gc)
+        if (major_gc && !deadlock_detect_gc)
             markQueuePushClosureGC(&gct->cap->upd_rem_set.queue, q);
         return;
     }

rts/sm/GC.c

@@ -104,6 +104,7 @@
  */
 uint32_t N;
 bool major_gc;
+bool deadlock_detect_gc;
 
 /* Data used for allocation area sizing.
  */
@@ -194,6 +195,7 @@ StgPtr mark_sp;            // pointer to the next unallocated mark stack entry
 void
 GarbageCollect (uint32_t collect_gen,
                 const bool do_heap_census,
+                const bool deadlock_detect,
                 uint32_t gc_type USED_IF_THREADS,
                 Capability *cap,
                 bool idle_cap[])
@@ -263,6 +265,9 @@ GarbageCollect (uint32_t collect_gen,
   N = collect_gen;
   major_gc = (N == RtsFlags.GcFlags.generations-1);
 
+  /* See Note [Deadlock detection under nonmoving collector]. */
+  deadlock_detect_gc = deadlock_detect;
+
   /* N.B. The nonmoving collector works a bit differently. See
    * Note [Static objects under the nonmoving collector].
    */

rts/sm/GC.h

@@ -17,9 +17,12 @@
 
 #include "HeapAlloc.h"
 
-void GarbageCollect (uint32_t force_major_gc,
+void GarbageCollect (uint32_t collect_gen,
                      bool do_heap_census,
-                     uint32_t gc_type, Capability *cap, bool idle_cap[]);
+                     bool deadlock_detect,
+                     uint32_t gc_type,
+                     Capability *cap,
+                     bool idle_cap[]);
 
 typedef void (*evac_fn)(void *user, StgClosure **root);
 
@@ -30,6 +33,8 @@ bool doIdleGCWork(Capability *cap, bool all);
 
 extern uint32_t N;
 extern bool major_gc;
+/* See Note [Deadlock detection under nonmoving collector]. */
+extern bool deadlock_detect_gc;
 
 extern bdescr *mark_stack_bd;
 extern bdescr *mark_stack_top_bd;

rts/sm/NonMovingMark.c

@@ -382,6 +382,11 @@ push (MarkQueue *q, const MarkQueueEnt *ent)
 void
 markQueuePushClosureGC (MarkQueue *q, StgClosure *p)
 {
+    /* We should not make it here if we are doing a deadlock detect GC.
+     * See Note [Deadlock detection under nonmoving collector].
+     */
+    ASSERT(!deadlock_detect_gc);
+
     // Are we at the end of the block?
     if (q->top->head == MARK_QUEUE_BLOCK_ENTRIES) {
         // Yes, this block is full.